The present invention relates to a cascade impactor, that is, an impactor that has a number of impactor stages in flow series for classifying particles according to “cut” sizes. Each impactor stage has a nozzle plate through which particle carrying fluid passes, and has a separate rotating impactor plate positioned below each nozzle plate. Each of the impactor plates is driven by a separate motor that can be controlled as to speed.
In the prior art, rotating impactor plates in an impactor apparatus are disclosed in U.S. Pat. No. 4,321,822. The device in U.S. Pat. No. 4,321,822 has a series of impactor plates positioned side-by-side, and they are all rotated through a gear arrangement from a single motor and drive shaft.